The invention relates generally to molded products with fastener elements for use in hook-and-loop fastening and the like.
Hook-and-loop fasteners typically have two components: a "loop" component with engageable fiber loops, either of a woven or non-woven fabric or matt, and a mating "hook" component with a large number of miniature fastener elements, sometimes of hook form or mushroom form, adapted to engage and retain the loops of the loop component. Although early hook components were woven, many advances have been made in their manufacture, such that now many hook components are economically molded, with the fastener elements integrally molded upon a common sheet-form base. Fischer, for example, teaches such a method in U.S. Pat. No. 4,794,028, in which the fastener elements are molded in individual closed cavities in a mold roll, and then stripped from their closed cavities by peeling the fastener "tape" from the surface of the mold roll. Molded fastener elements of fasteners intended for repetitive use are generally engineered with shapes and resins selected to provide an appropriate amount of strength and flexibility, such that the fastener will have the required retention strength and yet not tend to damage the engaged loops when peeled apart. Customarily, such sheet-form fastener components have been formed in continuous strips, and then cut and affixed to the surfaces wished to be separably joined.
In some cases, loop-engageable fastener elements have been injection molded as part of a relatively stiff product. For example, Mcvicker, in U.S. Pat. No. 5,656,226, illustrates an array of fastener elements being integrally molded with a surface of an ankle brace.
Although injection molding fastener elements integrally and in place upon a product avoids the step of subsequently attaching a strip of fastener "tape" to the product for assembly, such a process places some limitations upon the structure of the fastener elements that are not present with some continuous forming techniques. For example, filling very small fastener element cavities can require high pressures and fast flows to avoid chilling the resin before the cavities have sufficiently filled. Depending upon the size and geometry of the overall injected product, filling an array of such cavities in a relatively small region of a surface of the product can complicate the design of the gate and runner systems. If the entire mold cavity is filled in one shot, the molten plastic may initially flow across the openings of the fastener element cavities, without completely filling them. The plastic may then cool to a temperature that prevents further flow or requires extremely high pressures to fill the cavities. In addition, one-shot injection of an entire product having a small array of miniature fastener elements from a single flow of resin requires the resin of the entire product to have qualities appropriate for fastener element strength and flexibility. In some instances there may be a more economical choice of resins for the bulk of the product which will be foregone in order to ensure reliable fastener elements, and in some other cases the quality of the fastener elements may be mitigated in the selection of a resin more suitable for the rest of the product.